The invention relates to a method for accessing a storage unit. Computer-aided search methods are known, in which what are known as lists are used, in which key values are used to record data sets, which contain the relevant value. For example the key may be the name of a person. The key value is for example the surname “Bauer”. The list for the value “Bauer” then contains data sets for people with the surname “Bauer”. The data sets usually also contain further data fields, for example the first name and a telephone number in addition to the surname. To facilitate the search for the data in the other data fields, what are known as inverted lists are used, the keys for which are different from what are referred to as the primary key. For example an inverted list for the key “Ralf” contains all the data sets for people with this first name. Inverted lists allow the computing times for a processor used in the search to be reduced considerably. Nevertheless the computing time can still be considerable, for example a number of minutes, in particular when there are several hundred thousand data sets.
It is also often necessary to search for just one substring, i.e. a string, which only contains some of the characters stored in a data field. Computer-aided search methods for searching for substrings generally require even more computing time than search methods for searching for complete strings, because there is usually no inverted list for the search string including a substring.
A string includes a number of characters, each of which is assigned a specific bit sequence based on a code system. The bit sequences of different characters have the same lengths, e.g. with ASCII (American Standard Code II) or different lengths, e.g. when using a Huffmann code.
A substring contains at least one character less than a complete string. A distinction is made between start strings, inside strings and end strings. A start string contains at least two consecutive characters, of which one character is at one end of a complete string, e.g. at the left end. An inside string contains at least two consecutive characters from the inside of a string, i.e. no peripheral characters. An end string contains at least two consecutive characters, of which one character is located at the other end of a complete string, e.g. the right end.
A search string is a string to be searched for, where applicable containing a search operator and/or a wildcard character. Known wildcard characters are “*” and “?”. The “*” replaces one or more characters. The “?” replaces one character.